1. Technical Field of the Invention
This invention relates generally to communication systems and more particularly to RFID systems.
2. Description of Related Art
A radio frequency identification (RFID) system generally includes a reader, also known as an interrogator, and a remote tag, also known as a transponder. Each tag stores identification or other data for use in identifying a person, item, pallet or other object or data related to a characteristic of a person, item, pallet or other object. RFID systems may use active tags that include an internal power source, such as a battery, and/or passive tags that do not contain an internal power source, but instead are remotely powered by the reader.
Communication between the reader and the remote tag is enabled by radio frequency (RF) signals. In general, to access the identification data stored on an RFID tag, the RFID reader generates a modulated RF interrogation signal designed to evoke a modulated RF response from a tag. The RFID reader then also generates an unmodulated, continuous wave (CW) signal to activate and power the tag. The RFID tag converts the CW signal into stored power to respond to the RFID reader and uses a backscattering technique in which the tag modulates and reflects the CW signal back to the RFID reader. The RF response from the tag includes the coded data stored in the RFID tag. The RFID reader decodes the coded data to identify or determine the characteristics of a person, item, pallet or other object associated with the RFID tag.
RFID systems typically employ either far field or near field technology. In far field technology, the distance between the RFID reader and the tag is great compared to the wavelength of the carrier signal. Typically, far field technology uses carrier signals in the ultra high frequency or microwave frequency ranges. In far-field applications, the RFID reader generates and transmits an RF signal via an RF antenna to all tags within range of the RF antenna. Tags employing far field technology RF coupling at microwave or UHF have been used in applications involving shipping units such as pallets or carton level tracking or other applications needing long-distance reads.
In near-field technology, the operating distance is usually less than one wavelength of the carrier signal, and the reading range is approximately limited to 20 cm or less depending on the frequency. In near field applications, the RFID reader and tag communicate via electromagnetic or inductive coupling between corresponding reader and tag coil antennas. Typically, the near field technology uses carrier signals in the low frequency range. Generally, tags employing near field technology operating at LF or HF have been used in applications involving item-level tagging for inventory control in the supply chain management or applications involving short range reads such as smart cards or vicinity credit cards, e.g. for access control or monetary use, passports, money bills authentication, bank documents, etc. Such applications do not need long range reads of the tags but may need more security provided by near field technology. In addition, near field technology is known for better performance on tags near fluids, such as fluid medications, wherein far field RF coupling tends to incur interference from the fluids.
Currently, an RFID reader consists of a controller or microprocessor implemented on a CMOS integrated circuit and a transmitter and receiver implemented on one or more separate CMOS, BiCMOS or GaAs integrated circuits. It is desirable to reduce the size and power consumption and cost of the RFID reader for both near field and far field applications. In addition, to avoid blocking RF component from the transmitted signal, currently RFID readers and tags operate wherein the RF signal from the reader to tag must end before the RF signal from the tag to reader can begin. This mode of operation is undesirable and slows communications between readers and tags. Therefore, a need exists for a highly integrated, low-cost RFID reader that can operate in with passive and active tags in both near field mode and far field mode while simultaneously transmitting and receiving.